Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $75.68   4.291%   $78.9274   $78.93   $78.95   $78.90  
  Purchase #2 $107.64   10.532%   $118.9766   $118.98   $119.00   $119.00  
  Purchase #3 $117.87   6.603%   $125.653   $125.65   $125.65   $125.70  
  Purchase #4 $134.97   8.816%   $146.869   $146.87   $146.85   $146.90  
  Purchase #5 $179.32   13.709%   $203.903   $203.90   $203.90   $203.90  
  Purchase #6 $144.26   3.338%   $149.0754   $149.08   $149.10   $149.10  
  Purchase #7 $91.35   7.873%   $98.542   $98.54   $98.55   $98.50  
  7 purchase totals = $851.09       $921.9464   $921.95   $922.00   $922.00